The overall objective is to understand the cellular and molecular bases of abnormal immune regulation in aging humans and Down's syndrome (DS). The autologous mixed lymphocyte reaction (AMLR) and B cell activation, proliferation and differentiation are used as models. In the AMLR, distinct subsets of T cells proliferate, produce and respond to soluble mediators, and express distinct immunoregulatory functions. Resting B cells are resistant to the effect of B cell growth factor (BCGF); however, after activation respond to BCGF by proliferation, therefore, direct response of B cells to BCGF would suggest in vivo activation of B cells. The specific aims are: (a) to study the proliferative and immunoregulatory functions of T cells and T cells subsets activated in T-non T and T-TA AMLR; (b) to study the production and influence of interleukin-1 (IL-1), IL-2 and BCGF; (c) to study the proliferation and differentiation of monoclonal antibody-defined B cells and B cell subsets; (d) to enumerate the numbers and proportions of T cell- and- B cell subsets, using monoclonal antibodies; and (e) to correlate the quantitative and/or qualitative abnormalities of immunoregulatory T cells and abnormalities of B cells with the presence or absence of autoantibodies. Approximately 80-90 each aging (greater then 65 years) and young (18-35) subjects and 40 patients (15-35 years) with DS will be studied. T and non T cells are separated by E-rosetting. T cell- and B cell subsets are positively and negatively selected using monoclonal antibodies (OKT4, OKT8 and FMC1, FMC7) and panning technique. T cells/T cell subsets activated in T-non T AMLR for 4 days (TA) are irradiated and used as stimulators in T-TA AMLR. T cells/T cell subsets activated in the T-non T and T-TA AMLR are treated with mitomycin C and examined for helper/suppressor functions against T cell proliferation in the AMLR and B cell differentiation for Ig synthesizing and secreting cells. The activity of IL-2 produced in the AMLR, BCGF produced by T cells activated by PHA or Con A and IL-1 produced by LPS-stimulated macrophages are studied on CTLL-6 cell line, on proliferation of anti-Mu activated B cells, and IL-1 dependent cell line respectively. Subsets of T- and B- lymphocytes are studied using a battery of monoclonal antibodies and FACS analyzer. These observations will help in understanding the mechanisms of immunodysregulation in aging and DS that could help in designing the approach(es) that could be utilized in postponing the phenomena and diseases associated with aging.